This invention relates to the processing of petroleum-based heavy oils and residual oils, particularly those derived from tar sands. More particularly this invention relates to reducing the viscosity and the sulfur content of tar sand oil so that it may be more readily pumped and processed by available petroleum processing equipment. This invention is especially concerned with the removal of phenolic oxygen and/or thiol sulfur from the polycyclic aromatic compounds found in heavy oils, residual oils and, particularly, tar sand oils.
Major tar sand deposits are found in the Athabasca region of Alberta in Canada, as well as, in Utah and Oklahoma of the United States and in Venezuela. To date, this source of oil has not constituted a significant portion of the crude oil utilized in the free world. The cost of extracting oil from the tar sands by currently available technology has not made it economically attractive. Further, the nature of the tar sand oil does not make the use of conventional petroleum processing feasible--this oil is highly viscous, high in sulfur and high in metals content. However, the increasing cost of crude oil makes tar sand oil increasingly attractive economically. This is particularly so if mining procedures to recover the tar sand oil and initial processing techniques to produce a less viscous tar sand oil with lower sulfur and metals content are available at commercially attractive costs. The upgrading of the tar sands oil in field gathering stations is highly desirable so that conventional crude oil pipeline and pumping equipment and petroleum processing equipment can be employed to produce consumer products.
A summary of some of the properties of typical tar sand oils is set forth in Table I below.
TABLE I ______________________________________ TAR SAND OIL PROPERTIES Polar Compounds Oxygen Sulfur (Phenol- Source Content, % Content, % containing), % ______________________________________ Athabasca 2.9 4.8 28 North Asphalt Ridge, 2.9 -- 20 Utah Oil Creek, Oklahoma 3.0 2.3 35 ______________________________________
Oxygen content is in the range of 1-3% and sulfur in the range of 4-6% and even as high as 12% for different tar sands. About 70-75% of the oxygen is phenolic oxygen. Sulfur is present predominantly as disulfide, thiophenes and heterocyclic sulfur. Very little thiol sulfur is found, as such, since it readily forms disulfide linkages which are easily broken during subsequent processing. For purposes of the present disclosure and claims the term "phenolic oxygen" is used to identify the oxygen in the -OH group attached to polycyclic aromatic compounds and the term "thiol sulfur" is used to identify the sulfur in the -SH group attached to polycyclic aromatic compounds. As used herein, the term "polycyclic compounds" includes dicyclic compounds. Unless stated otherwise, percent, as used in this disclosure and claims, is weight percent.
The phenolic OH found in the polycyclic aromatic compounds of tar sand oil causes a significant increase in the oil's viscosity due to hydrogen bonding. Thiol sulfur found in similar compounds is also undesirable because of the deleterious effect it has on petroleum processing catalysts which it can rapidly and irreversibly deactivate. Additionally, this sulfur greatly increases the corrosiveness of the heavy oil.
It is an object of the present invention to produce a heavy oil having a lower phenolic oxygen and/or thiol sulfur content so that the oil may be transported and processed in conventional pumping and processing equipment currently employed in the petroleum industry.